Anatomy Of A Bloodsucker

Another mosquito bite on a hot Florida night, and another squashed insect. We don't give these annoying critters much thought, except to kill them and wipe away the blood.

But don't dismiss the tenacity of this entomological wonder. Mosquitoes make up a massive army that has survived millennia through adaptation and sheer numbers. In their hunger for blood, mosquitoes become vectors of malaria, dengue and encephalitis, killing more people each year than any other organism.

Despite global eradication programs, mosquitoes have survived remarkably well, says Phil Koehler, an entomologist at the University of Florida in Gainesville.

"They're well adapted for survival," he says. "Some salt marsh mosquitoes, which are a nuisance along the coasts of Florida, lay eggs that survive drying out. They can remain out of water for five years and hatch."

Mosquitoes are streamlined and slender, with six flexible legs designed for soft, stealthy landings on their prey. They scan the landscape with two massive, compound eyes equipped with multi-focused lenses, and a pair of navigational antennae. Special location sensors detect carbon dioxide exhaled by their prey.

Powerful wings that beat more than 500 times per second allow the mosquito to change direction in an instant. The insect breathes through a series of small holes along the abdomen, which also cool its high-torque heart.

"You have to admire any group of organisms that's so successful and so widely distributed," says Chet Moore, an entomologist at Colorado State University and an international expert on insect-transmitted disease. "The mosquito has developed its own set of specializations."

Mosquitoes are masterpieces of natural engineering, Moore says. But their design also is lethal. The most unique part of their body is a needlelike appendage called a proboscis, which acts like a straw to suck blood from the skin of a person or animal.

The female mosquito excretes a special chemical in its saliva to keep the blood from clotting. In this saliva percolates myriad bacteria and viruses that have killed untold billions of people throughout the ages. Male mosquitoes are less fearsome: They drink only the nectar and juices from plants.

Over time, humans and animals have developed their own strategies to combat mosquitoes, but the insects always seem to be one step ahead of them.

"The evolution of mosquitoes has a lot to do with the evolution of their hosts," Moore says. "Mosquitoes have evolved to take advantage of them. They are very efficient at what they do."